How many words do you see every day? Thousands? Tens of thousands? Newspaper and website headlines, emails, tweets, street signs, books, Nooks, Kindles, magazines — to a degree unmatched in human history, we are surrounded by words. We’re inundated by written instructions, admonitions, advertisements, entertainments. In fact, it sometimes seems as if our world is made not of bricks and mortar, but of infinitely rearranged letters.

“The universe is made of stories, not of atoms,” the American poet Muriel Rukeyser once wrote, and more and more, as time goes by, that sounds about right.

But what if paying strict heed to every written word that one saw every single day meant the difference between survival and annihilation? What if the misreading of a sign on an unfamiliar road, for example, meant not the inconvenience of a missed turn, but a sudden, violent death?

Here, LIFE.com takes a look at some of the countless signs that troops encountered during the course of World War II, from the islands of the Pacific to the deserts of North Africa to the ruined cities of Europe. Official warnings; adamant instructions; wry, handwritten inside jokes — all of them silent reminders of a conflict that, until the very end, dished out one paramount, universal command: Pay attention!